OFR 151.pdf - CRC LEME

6.2 Australian backdrop
Late Cretaceous sediments are preserved in most of the continental margin basins in southern,
western and northern Australia. However the palaeobotanical record in northern Australia is
usually discontinuous, due to limited sampling, sediment starvation and/or poor preservation
of miospores in bioclastic carbonates. Consequently much of the detailed information on
flora and vegetation comes from southeastern Australia where quasi-continuous pollen and
spore sequences are preserved in the Gippsland and Otway Basin (cf. Dettmann 1994,
Douglas 1994).
Elsewhere, fossil evidence is preserved in thin (and fortuitously preserved) carbonaceous
deposits. For example, an unusually diverse macroflora is preserved in the Cenomanian
Winton Formation in the Eromanga Basin. Turonian to Maastrichtian sediments in this basin
usually preserve the cuticular remains of conifers and angiosperms but as yet these have not
been systematically studied. The majority of Late Cretaceous microfloras represent coastal or
floodplain communities or shoreline vegetation around deep freshwater lakes at the palaeosouthern
(polar) end of the Australo-Antarctic Rift System, such as in the Gippsland and Bass
Basins.
6.3 Late Cretaceous floras
6.3.1 Evolution and migration
Late Cretaceous microfloral provinces, including those encompassing Australia and
neighbouring landmasses have been reviewed by Herngreen and Chlonova (1981). Coastal
areas and rift valley systems at high latitudes may have been important in the adaptive
radiation of species that subsequently migrated into lower latitudes (references in Lewin
1983, Hill and Scriven 1995). Rift valleys are likely to have been pathways for the migration
of taxa adapted to disturbed environments as well as forming geographic barriers between
formerly widespread populations (Hill et al. 1999).
Most of the plant genera that evolved or migrated into the Australian region during the late
Early and Late Cretaceous were angiosperms but several modern gymnosperms and ferns also
appear at this time. Examples (fossil genera in parentheses) include Lagarostrobos
(Phyllocladidites mawsonii) in the Turonian, and Dacrydium (Lygistepollenites florinii) and
Nothofagus (Nothofagidites) in the Campanian. Fossil spores preserved on the South
Shetland Islands confirm that the migration of ground-ferns such as Ruffordia
(Appendicisporites) and Lophosoria (Cyatheacidites) from western into eastern regions of
Gondwana was time-transgressive (Dettmann 1986b, Helby et al. 1987, Dettmann et al. 1992,
Hathaway et al. 1999).
Many of the taxa which first appear on the palaeo-northern margin (North West Shelf) during
the Late Cretaceous are not recorded in central or southern basins until the Late Paleocene or
Early Eocene, e.g. Anacolosa (Anacolosidites acutullus). This diachronism is likely to reflect
differences in vagility as well as climatic forcing. Many of the angiosperms that became
extinct at the Cretaceous/Tertiary boundary are likely to have been insect-pollinated
(Macphail 1994a).
6.3.2 Plant competition
The adaptive radiation of the angiosperms during the late Early and Late Cretaceous initiated
the wholesale reorganisation of most terrestrial ecosystems. Their competitive success
reflects their superior reproductive strategies relative to gymnosperms and cryptogams,
irrespective of climatic or edaphic forcing (Stewart 1983, Lupia et al. 1999). Bawa (1995)
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